Along with the recent miniaturization of semiconductor devices, a micropattern has been drawn on a photomask by exposure using an electron beam exposure apparatus.
As one of such electron beam exposure apparatuses, a multi-column electron beam exposure apparatus has been proposed, in which a plurality of column cells for irradiating electron beams are arranged.
The multi-column electron beam exposure apparatus has a processing speed faster than a single-column electron beam exposure apparatus, since the multi-column electron beam exposure apparatus performs exposure with the plurality of column cells in parallel.
However, in the multi-column electron beam exposure apparatus, restrictions on mechanical working accuracy, and the like cause aberration of an electron optical system, effective current density of the electron beam, an aperture size of an exposure mask (rectangular aperture), and the like to vary among the column cells. For this reason, even when the same pattern is exposed for the same exposure time, the finished line width varies among the column cells.
To counter such a situation, it is conceivable to measure the finished line width of each column cell and to correct the exposure time of each column cell so as to achieve a uniform line width.
However, the exposure using the electron beam involves a so-called proximity effect in which a line width of a pattern varies due to a change in backscattering amount of the electron beam according to the pattern density. For this reason, in the electron beam exposure apparatus, the exposure time is changed according to the pattern density to correct the proximity effect.
However, the variation in line width among the column cells cannot be prevented, when the exposure time is changed for proximity effect correction and the like, just by matching the exposure time of each column cell with a specific finished line width as described above.
Moreover, as another correction method, it is conceivable to correct a variation in line width among the column cells by utilizing proximity effect correction calculation. In this case, a forward scattering length, a backscattering length and scattering intensity specific to each column cell are experimentally set so as to achieve a uniform line width among the column cells. Thereafter, the exposure time of each column cell is calculated by performing proximity effect correction calculation based on such parameters.
However, the proximity effect correction calculation performed under specific conditions for each column cell increases the complexity, which results in an increase in the time to generate the exposure data. Moreover, a large number of pieces of exposure data specific to each column cell needs to be managed, which is not practical.
The three parameters for the proximity effect correction calculation cannot achieve enough degree of freedom to correct the causes of the variation in line width, such as the proximity effect, the aberration of the electron optical system, the effective current density of the electron beam and the aperture size of the exposure mask. For this reason, accurate correction cannot be performed.